CIS3931

1
CIS3931 Intro to JAVA

• Lecture Note Set 1
• Thursday 12-May-05

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A basic JAVA program

• // Class declaration
• public class Welcome1
• public static void main( String args )
• System.out.println(Welcome to Java)
• //end of main method
• //end of class

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Compiling a JAVA program

• Command javac ltfilename.javagt
• Compiler will potentially return with error
  messages
• Error messages time to debug your code
• Debugging Correcting syntax errors in your code
• No errors runtime testing

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Running a JAVA program

• java ltfilenamegt
• Example to run the class file example.java you
  would type java example
• Runtime testing Making sure your program
  performs as expected

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Variables

• A place to store values in memory
• Many different types
• int integer A whole number value (ex 12)
• char character A single character (ex c)
• String characters (ex hello)
• float floating point number (ex 3.14)

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Variable examples (declarations)

• int a 1 //assigns the value 1 to a
• int b 1 1 //assigns the result of 1 1 to b
• int c a b //assigns the result of a b to c
• a 1 //assigns the result of a 1 to a
• String cup new String(cup of Java)
• // assigns the literal cup
  ofJava to cup

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Variable Casting

• It is possible to cast one variable type to
  another
• Example A character is actually just a special
  case of an integer
• The character A has the integer value 65

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Text Formatting

• Text is printed to the screen with either of the
  following commands
• System.out.println(Insert Text Here)
• System.out.print(Insert Text Here)
• System.out.print(hello\n) is equivalent to
• System.out.println(hello)

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Text formatting

• Column formatting can be accomplised with the /t
  escape character
• Example
• System.out.println(a\tb\tc\td)

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Comments

• There are two types of comments in JAVA
• Single line comments
• //This is a single line comment
• Block comments
• / This is a
• block comment/

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The JAVA API

• http//java.sun.com/j2se/1.5.0/docs/api/
• The most useful tool when programming in JAVA
• Many algorithms and functions are already written
  for you

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Using the API

• You have to import the class that contains the
  functions you want to use
• Example
• Import java.io. will allow you to use anything
  in the java.io class

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User Input

• Use BufferedReaders.
• BufferedReader br new BufferedReader(new
  InputStreamReader(System.in))
• String input br.readLine()
• int num1 Integer.parseInt(input)
• BufferedReader is in java.io.